In a circuit board of a liquid crystal display panel, a gamma reference voltage is used to obtain a gray-scale voltage through an internal divider resistor network of a source driver. Voltages applied to liquid crystal molecules are actually differences of different gray-scale voltages and a common electrode voltage (VCOM). In order to prevent aging of liquid crystal material, the voltages applied to two ends of the liquid crystal molecules are not allowed to have a direct current component. When entering a next frame after completion of scanning of a previous frame, it is needed to change polarities of the voltages applied to the liquid crystal molecules, thus, under ideal conditions, for a certain gray-scale image, there are two voltages including a positive voltage and a negative voltage relative to VCOM, the two voltages have same charge and opposite polarities.
However, in practical work, when a voltage of a gate line is changed, correctness of voltages of pixel electrodes may be affected through a parasitic capacitance between the gate line and the pixel electrodes, resulting in that positive and negative display areas are asymmetrical with respective to VCOM, thereby applying a direct-current component ΔVp on the pixel electrodes.
A current liquid crystal panel is designed to compensate the asymmetry of the positive and negative display areas caused by the direct-current component ΔVp by adjusting VCOM. However, such an adjustment is usually performed only one time. When the liquid crystal panel is used in a client terminal, ΔVp in the liquid crystal panel may be changed due to displaying a fixed screen for a long time, in a hot and humid environment and leakage current of a thin film transistor (TFT). Thus, there is a deviation between an actually adjusted VCOM and an ideal VCOM of the panel. Even under conditions of constant gray-scale voltages, the positive and negative display areas are asymmetrical with respective to VCOM. There is also a deviation in data of the positive and negative areas, and this deviation is a direct-current component; when this direct-current component is applied to the liquid crystal display panel for a long time, a residual image may appear due to characteristics of the liquid crystal molecules.